摘要:

AbstractA random sampling procedure is used to construct resonances in the unresolved region. The success of this procedure depends on the ability to determine statistically meaningful reactivity coefficients. To establish an estimate of the statistical dispersion of the Doppler effect for a carbide-fueled fast power reactor, many different resonance ladders were studied for each total angular momentum state of the compound nucleus for each isotope. It is shown that the one-standard-deviation statistical uncertainty in the calculated total Doppler effect for the core is∼3%, which is quite satisfactory. However, the statistical uncertainty in the239Pu Doppler effect was determined to be∼40% in the unresolved region, and∼35% over all energy. The manner in which the ladders are chosen is investigated, with the conclusion that any ladder, giving the proper distributions of resonance parameters, may be used. Based on these results, it may be advantageous to use the random sampling method of resonance construction in place of the usual statistical averaging procedure. This would eliminate some of the approximations inherent to these statistical averaging procedures, by includingallinterference and overlap effects.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19680

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractCorrelated neutron fluctuation experiments have been performed on a poorly coupled, multiple seed-blanket reactor and on a better coupled cylindrical lattice reactor. The fluctuating numbers of counts recorded in various gate times by separated detectors are analyzed in terms of a proposed measure of reactor coupling, the modified coefficient of correlation,MCC, as well as in terms of the conventional dispersion parameterY. Effects of count losses, statistical bias, and statistical error are examined. Calculations ofMCCandYare carried out in theα-mode form of the product density formalism for a number of detailed reactor models, including several four-energy-group diffusion theory andP-3 transport models for reactor design. Two of these detailed models, incorporating reduced fast-neutron transport and removal cross sections, are in agreement withMCCmeasurements, while one design model is not.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19681

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe problem of computing the time-dependent reactivity from flux measurements is solved for a stochastic-point-reactor model using linear estimation theory. In order to use this method, an appropriate reactivity model must be formed which can be embedded into the reactor system as one of its state variables. A digital filter, designed using Kalman-Bucy filter theory, operates on the sampled neutron-density output of the stochastic reactor and provides estimates of the state variables of the system, one of which is the reactivity. Digital Computer results are used to show the response of the Kalman filter in computing the reactivity from stochastic-neutron-density measurements. The results show that this analytical filter can be used to determine the reactivity from neutron density which has a certain noise content due to the stochastic processes involved in the reactor system.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19682

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThis work is a study of approximate methods for the solution of problems in space-dependent nuclear reactor dynamics. It is shown that these approximate methods can all be considered applications of the method of weighted residuals. In each method, a trial solution is formed for the neutron flux by making expansions in known spatially dependent functions called trial functions. Each approximate method differs from the others in the manner in which its trial functions are chosen. The undetermined time-dependent functions, called amplitude functions, are then found by using the weighted-residual procedure known as the method of undetermined functions to derive the so-called multimode kinetics equations, which are first-order ordinary differential equations in time. The multimode kinetics equations are then integrated using the method of undetermined parameters. Weighted-residual procedures are thus used for both spatial and temporal integrations. Some numerical results are reported for continuous synthesis and multichannel systhesis approximations. Several choices of weighting functions are compared. Conclusions are drawn regarding the roles of the trial functions and the weighting functions in obtaining accurate solutions.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19683

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA new method for the solution of the Boltzmann equation for time-dependent or stationary neutron transport is presented. The essentials of the method are a Fourier transform of the transport integral equation and the decomposition of the new kernel into a bilinear form. In the monoenergetic case, the transport problem is reduced to the solution of an (infinite) linear system of equations. It is important that the matrix elements in this linear system be determined only once for any geometry and that this be done in an analytical way. In the present paper, the matrix elements for plane, spherical, and cylindrical geometries are constructed explicitly and are presented in a form suitable for numerical applications. To illustrate the efficiency of the method, the critical dimensions for these geometries have been determined in various integral transformITNapproximations,Nbeing the order of the linear system after truncation. For samples of a thickness up to∼10 mean-free-paths, the results for the critical dimension in stationary problems, or for the fundamental time-decay constants in nonstationary problems, have in theIT4approximation, at least, the accuracy of the correspondingS16results.The convergence of theITNresults, with respect to the orderN, is very fast. The results forN= 4 can be considered as exact within one or two units in the fifth digit. The convergence behavior of theSNand thePNmethod is decidedly slower. In contrast to theSN, PNor Case’s method, the smaller the system, the better the accuracy of theITNcalculations for fixedNis. The increase in accuracy by increasingNrequires less computational effort for theITNapproximation than forSNorPNapproximation. Apart from providing an analytical standard for the check of numerical approximations, the present method is a simple and rigorous tool for the calculation of neutron distributions, particularly in small systems.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19684

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractExpressions for point source Green’s functions are developed which mathematically describe monoenergetic, neutral particle transport in uniform, unbounded media with particle absorption and azimuthally symmetric scattering of finite-degree polar angle anisotropy. The method of development follows closely the plane source superposition technique of Fano, Spencer, and Berger with the extension of explicit formulation of the relevant plane symmetry functions. Some limit properties of the derived Green’s function are considered.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19685

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractCriticality codes are in general adjusted to reproduce measured values of critical bucklings which furnish (k∞−1)/M2. The parameter adjusted isk∞, the calculation of leakage being assumed to be well made. However, in the case of heterogeneous systems in particular, the slowing down region is not easy to study, and one has perforce to make certain simplifying assumptions which reflect on the calculated value of the age. Since a proper estimation of leakage is necessary for a code adjusted on clean critical systems to be valid when extrapolated to large power reactors where leakages are different, it is of practical interest to be able to use some experimental data for checking age calculations and searching for improvements if necessary. Pulsed experiments furnish the necessary experimental data, since measurements made on a given lattice for different block sizes permit the separation of multiplication from leakage. A method of analysis is presented and applied to experiments on natural uranium/graphite lattices. An effective age-diffusion expression in whichk∞/p, L2and the mean lifetimeloare evaluated in terms of buckling-dependent spectra, is transformed into a linear equation which permits simultaneous adjustment ofpand of the age. Our analysis shows that pulsed experiments can be sufficiently precise for age adjustments. However, since these experiments are performed at far-from-critical bucklings, the precision is not sufficient for adjustingp, and hencek∞. We conclude that these experiments are very useful for adjusting leakage, but this adjustment being made, critical experiments remain necessary for the subsequent adjustment ofk∞with precision.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19686

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe energy distribution of neutrons from proton-nucleus nonelastic collisions for 18-MeV protons on14N,27Al,56Fe,181Ta, and208Pb and for 15-MeV protons on27Al and208Pb have been calculated with the intranuclear-cascade-evaporation model of nuclear reactions and with the evaporation model of nuclear reactions. Comparisons between the calculated neutron spectra and experimental data are presented, and it is shown that neither model is entirely reliable in the energy region considered but that the intranuclear-cascade-evaporation model is the more reliable of the two.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19687

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractUsing the sphere transmission and time-of-flight techniques, the neutron spectra emitted from 0.58 and 3.0 mfp of nitrogen and from 0.72 mfp of oxygen have been measured for a 14-MeV neutron source. The analysis of the data has been done using the Livermore Monte Carlo Neutron-Transport Program (SORS). Good agreement was obtained for nitrogen with a revised SORS calculation, where five inelastic levels are explicitly included in the computational routine for the (n,n′) cross sections. To obtain agreement between calculations and measurements for oxygen, the computational model had to be extended so that it could account for the presence of inelastic levels. A revision of the cross sections was also carried out. With these new versions of SORS, excellent fits to the experimental measurements for nitrogen and oxygen were obtained. Using the revised SORS program, calculations for the transport of neutrons in air from a 14-MeV point neutron source were obtained.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19688

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractWe have obtained gamma-ray spectra for the reactions16O(n,n′γ)16O and16O(n,αγ)13C for incident-mean-neutron energiesEnbetween 6.7 and 11.0 MeV. The gamma rays were detected using a 30 cm3coaxial Ge(Li) detector placed at 55 and 90 deg with respect to the incident-neutron direction. Time-of-flight electronics was used with the gamma-ray detector to discriminate against unwanted pulses due to neutrons and background gamma radiation. Two samples of 75 and 31 gm of BeO in the form of right circular cylinders were used. The incident-neutron beam was produced by bombarding a deuterium-filled gas cell with a pulsed deuteron beam of appropriate energy; forEn≤8.5 MeV the deuteron beam was obtained from the ORNL 6-MV Van de Graaff, and forEn≥8.5 MeV it was obtained from the ORNL Tandem Van de Graaff. These data have been reduced to differential cross sections for production of gamma rays from16O. The cross sections have been compared, where possible, with previously measured values with reasonable agreement. However, there are several important differences, and these are discussed. Summing the partial cross sections yields values for the total nonelastic cross section which are in good agreement with values for the nonelastic cross section obtained from the difference between the total cross section and the total elastic cross section.

ISSN:0029-5639    

DOI:10.13182/NSE70-A19689

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor